Water soluble thermosetting polyester resin composition and method of preparing the same

Abstract

A water soluble thermosetting polyester resin composition for undercoating a PCM steel sheet is prepared from about 100 parts by weight of thermosetting polyester resin obtained by condensing polyethylene terephthalate using glycol and polybasic acid, about 5-20 parts by weight of anhydrous polybasic acid and amine. A paint composition prepared using thus prepared resin composition is applicable for undercoating PCM steel sheet for both of home appliances and construction materials. In addition, an organic solvent included in the conventional oily paint composition can be excluded to minimize an environmental contamination, a dangerous factor of initiating fire and a bodily harm on human. Further, a paint composition having advantageous processibility, chemical resistance, solvent resistance, adhesion and scratch resistance may be prepared.

1. A water soluble thermosetting polyester resin composition for undercoating a pre-coated metal steel sheet, prepared by:
 reacting terephthalic acid with ethylene glycol in a molar ratio of terephthalic acid to ethylene glycol of about 1:1 to about 1:1.4 to produce polyethylene terephthalate; 
 condensing the polyethylene terephthalate with a glycol and a polybasic acid to produce a thermosetting polyester resin; 
 reacting about 100 parts by weight of the thermosetting polyester resin with about 5-to about 20 parts by weight of an anhydrous polybasic acid to produce a product; and 
 adding an amine into the product until the pH of the product is about 7 to about 9. 
 
     
     
       2. The water soluble thermosetting polyester resin composition of  claim 1 , wherein the thermosetting polyester resin has an acid value of about 20- to about 30, a hydroxyl value of about 50- to about 120, and a molecular weight of about 8,000- to about 20,000. 
     
     
       3. The water soluble thermosetting polyester resin composition of  claim 1 , wherein the thermosetting polyester resin composition has an acid value of about 60- to about 80, a hydroxyl value of about 50- to about 120, and a water diluting property of about at least 300%. 
     
     
       4. A method of preparing a water soluble thermosetting polyester resin composition for undercoating a pre-coated metal steel sheet, comprising:
 reacting terephthalic acid with ethylene glycol in a molar ratio of terephthalic acid to ethylene glycol of about 1:1 to about 1:1.4 to produce polyethylene terephthalate; 
 condensing the polyethylene terephthalate with a glycol and a polybasic acid to produce a thermosetting polyester resin; 
 reacting about 100 parts by weight of the thermosetting polyester resin with about 5 to about 20 parts by weight of an anhydrous polybasic acid through a ring opening addition or condensation polymerization reaction to produce a product; and 
 adding an amine into the product for neutralization until the pH of the product is about 7 to about 9. 
 
     
     
       5. The method of preparing a water soluble thermosetting polyester resin composition of  claim 4 , wherein the thermosetting polyester resin is prepared by using a glycol and a polybasic acid with a molar ratio of the glycol to the polybasic acid of about 1:1 to about 1:1.1, and further wherein the thermosetting polyester resin has an acid value of about 20- to about 30, a hydroxyl value of about 50- to about 120, and a molecular weight of about 8,000- to about 20,000. 
     
     
       6. The method of preparing a water soluble thermosetting polyester resin composition of  claim 4 , wherein the glycol is at least one selected from the group consisting of ethylene glycol, propylene glycol, 1,4-butylene glycol, 1,6-hexanediol, neopentyl glycol, methylpropanediol, cyclohexane dimethanol, hydrogenated bisphenol A, ethylene oxide added bisphenol A, propylene oxide added bisphenol A, ethylene oxide added bisphenol F, propylene oxide added bisphenol F, ethylene oxide added bisphenol S, and propylene oxide added bisphenol S. 
     
     
       7. The method of preparing a water soluble thermosetting polyester resin composition of  claim 4 , wherein the polybasic acid is at least one selected from the group consisting of isophthalic acid, terephthalic acid, adipic acid, azelaic acid, sebacic acid, and cyclohexane diacid. 
     
     
       8. The method of preparing a water soluble thermosetting polyester resin composition of  claim 4 , wherein the anhydrous polybasic acid is at least one selected from the group consisting of anhydrous maleic acid, anhydrous phthalic acid, anhydrous tetrahydrophthalic acid, and trimellitic anhydride. 
     
     
       9. The method of preparing a water soluble thermosetting polyester resin composition of  claim 4 , wherein the amine is at least one selected from the group consisting of ethylene diamine, dimethyl ethanolamine, triethylamine, diethanolamine, triethanolamine, monoethanolamine, diethylethanolamine, diethylene diamine, monoethylamine, dipropyl ethanolamine, diethyl cyclohexylamine, diethylene triamine, dioctylamine, and dioctyl aminoethanol. 
     
     
       10. The method of preparing a water soluble thermosetting polyester resin composition of  claim 4 , further comprising adding deionized water for preparing a water soluble thermosetting polyester resin composition having a solid content of about 50- to about 60% percent by weight after adding the amine. 
     
     
       11. The method of preparing a water soluble thermosetting polyester resin composition of  claim 10 , wherein the thus prepared water soluble thermosetting polyester resin composition has an acid value of about 60- to about 80, a hydroxyl value of about 50- to about 120, and a water diluting property of about at least 300%. 
     
     
       12. The water soluble thermosetting polyester resin composition of  claim 1 , wherein the polyethylene terephthalate has a molecular weight of about 1,500- to about 2,000.